1. Field of the Invention
The present invention relates to a flat display using Liquid Crystal (LC), EC or the like to realize a larger scale screen.
2. Description of the Prior Art
Heretofore, there are two methods for driving displays such as liquid crystals or like, that is, an active method and a passive method. The active method is extremely superior to the passive method in indicating characteristics such as picture quality, response characteristic and like. In practice, a large scale flat display can not be commercially available because its manufacturing is very hard. Formations of display cells being driven by active elements were developed by many manufacturers such as Sharp and Hitachi corporations since seventy eras based on semiconductor manufacturing technologies.
A typical flat display comprises a matrix of display cells each having common and lower electrodes, a matrix of transistors each having a collector connected to the lower electrode of the corresponding cell, column lines each connected to emitters of corresponding transistors in alignment with Y direction, and row lines each connected to bases of corresponding transistors in alignment with X direction. The lower electrodes, the transistors, the column and row lines are provided on a common glass substrate.
Therefore, semiconductor materials are stacked or covered on the substrate to provide an npn structure. The npn structure is partitioned into areas of the lower electrodes, the transistors and the column lines by lithography and photoetching. The remaining area is then oxygenated to provide a grid or grooves of silicon dioxide. The metallic row lines are coated on the npn structure after covering an insulation layer. Connections among the transistors, metallic column lines and lower electrodes are performed by contact hole technique.
This process is made by using technologies for manufacturing semiconductor chips such as photo-lithography, etching and plasma CVD (Chemical Vapor Deposition) methods. In conventional methods, a matrix of transparent pixel electrodes, wirings and a matrix of active elements such as transistors are provided on the glass substrate having a size, for example, six by eight inches. The transistors must be provided on the glass substrate with low density upon manufacturing large scale displays.
The transistors then occupy small area of the glass substrate after finishing, and are disposed with considerably long distance ratio. It is therefore difficult to unify characteristics of the transistors each provided on the glass substrate.
Yield of the flat display having uniform transistors also is reduced as well as increasing invested capital because the transistors must be provided on the large scale glass substrate with uniform characteristics. Therefore, the large scale flat display can not be commercially available by now.
As described above, there are conventional problems that yield of the flat display having pixels with uniform characteristics is low because the matrix of the transistors must be provided on the glass substrate with extremely low density by using semiconductor process. The manufacturing apparatus dealing with large-scale semiconductor wafers is very expensive to produce a large size display.